This invention relates to multi-channel gain controls and methods of controlling the gain in a multi-channel system. An example of an application of the invention is as a gain control in radar or sonar systems having more than one receiving channel.
The simplest form of a multi-channel gain control comprises a number of variable attenuators having substantially identical characteristics which are mechanically ganged. To achieve with certainty tracking errors (i.e., gain differences) less than 5% over even a limited dynamic range of gain, it is necessary to use "high precision" controls. Such controls are expensive and bulky. Furthermore, as the maximum attenuation possible is limited by the stray coupling between the attenuator input and output circuits it may be necessary to carry out the attenuation in two or more isolated stages to achieve an adequate dynamic range of gain. When multi-channel attenuation is required with very low tracking errors a wide range of attenuation can only be achieved at great cost and complexity.
An application of a precise multi-channel gain control is in radar or sonar systems having two or more receiving channels to provide source direction information. In such systems it is essential to be able to vary the gains of each channel in precise synchronism, as unequal channel gains will produce directional errors. An example of a sonar system of this type is that described in U.S. Pat. No. 3,366,922 which relates in particular to a binaural sensory aid for blind persons. Two receiving channels are used in these aids and the use of conventional precision ganged attenuators is not compatible with the special packaging requirements.